# Cobalt

properties
[ Ar ] 3 d 7 4 s 2
27 Co
General
Name , symbol , atomic number Cobalt, Co, Jan.
Element category Transition metals
Group , period , block 9 , 4 , d
Appearance metallic with a bluish-greyish hue
CAS number 7440-48-4
EC number 231-158-0
ECHA InfoCard 100.028.325
Mass fraction of the earth's envelope 37 ppm
Atomic
Atomic mass 58,933194 (4) et al
Atomic radius (calculated) 135 (152) pm
Covalent radius low-spin: 126 pm, high-spin: 150 pm
Electron configuration [ Ar ] 3 d 7 4 s 2
1. Ionization energy 7th.88101 (12) eV760.4 kJ / mol
2. Ionization energy 17th.0844 (12) eV1 648.39 kJ / mol
3. Ionization energy 33.50 (6) eV3 232.3 kJ / mol
4. Ionization energy 51.27 (10) eV4 947 kJ / mol
5. Ionization energy 79.50 (20) eV7 671 kJ / mol
Physically
Physical state firmly
Modifications 2
Crystal structure hexagonal
density 8.90 g / cm³ (20 ° C )
Mohs hardness 5.0
magnetism ferromagnetic
Melting point 1768 K (1495 ° C)
boiling point 3173 K (2900 ° C)
Molar volume 6.67 · 10 −6 m 3 · mol −1
Heat of evaporation 390 kJ / mol
Heat of fusion 17.2 kJ mol −1
Speed ​​of sound 4720 m · s −1
Specific heat capacity 421 J kg −1 K −1
Work function 5.0 eV
Electric conductivity 16.7 · 10 6 A · V −1 · m −1
Thermal conductivity 100 W m −1 K −1
Chemically
Oxidation states 2 , 3
Normal potential −0.28 V (Co 2+ + 2 e - → Co)
Electronegativity 1.88 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP
55 Co {syn.} 17.53 h ε 3.451 55 feet
56 Co {syn.} 77.27 d ε 4,566 56 feet
57 Co {syn.} 271.79 d ε 0.836 57 feet
58 Co {syn.} 70.86 d ε 2.307 58 feet
59 Co 100% Stable
60 Co {syn.} 5.2714 a β -γγ 0.31 + 1.17 + 1.33 60 Ni
61 Co {syn.} 1,850 h β - 1.322 61 Ni
For other isotopes see list of isotopes
NMR properties
Spin
quantum
number I
γ in
rad · T −1 · s −1
E r  ( 1 H) f L at
B = 4.7 T
in MHz
59 Co 7/2 0+6.332 10 7 0.278 047.36
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary

danger

H and P phrases H: 350i-334-317-413
P: 273-280-304 + 341-342 + 311-302 + 352
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .

Cobalt (chemical terminology; latin Cobaltum , standard language cobalt ; from Erstbeschreiber after the cobalt ore as a starting material Cobalt Rex named) is a chemical element with the element symbol Co and the atomic number 27, Cobalt is a ferromagnetic transition metal of Group 9 or cobalt group of the Periodic Table . In the older counting method it belongs to the 8th subgroup or iron-platinum group .

## history

Cobalt ores and cobalt compounds have been known for a long time and were primarily used as cobalt blue ( Thénards Blau and Zaffer ) for coloring glass and ceramics . In the Middle Ages they were often thought of as valuable silver and copper ores . However, since they could not be processed and because of the arsenic content gave off bad smells when heated, they were viewed as bewitched. Allegedly goblins ate the precious silver and excreted worthless silver-colored ores in its place . In addition to cobalt, these were also tungsten and nickel ores. These ores were then nicknamed by the miners with nicknames such as nickel, tungsten (for example "Wolfs-Schaum", lat. Lupi spuma ) and Kobold ore, i.e. cobalt. In 1735, the Swedish chemist Georg Brandt discovered the previously unknown metal while processing cobalt ores, described its properties and gave it its current name. In 1780, Torbern Olof Bergman discovered that cobalt is an element while studying its properties more closely.

## properties

### Physical Properties

Crystal structure of α-Co, a = 250.7 pm, c = 406.9 pm

Cobalt is a steel-gray, very tough heavy metal with a density of 8.89 g / cm³. It is ferromagnetic with a Curie temperature of 1150 ° C. Cobalt occurs in two modifications : a hexagonal densest ( hcp ) crystal structure in the space group P 6 3 / mmc (space group no.194 ) with the lattice parameters a = 250.7 pm and c = 406.9 pm as well as two formula units per Unit cell and a face-centered cubic shape ( fcc ) with the lattice parameter a = 354.4 pm. The hcp modification (α-cobalt, historically ε-cobalt) is stable at lower temperatures and converts to the fcc modification (β-cobalt, historically α-cobalt) at approx. 450 ° C.

As a typical metal , it conducts heat and electricity well; its electrical conductivity is 26 percent of that of copper .

The atomic mass of naturally occurring cobalt is a special feature; At 58.93 it is greater than the mean atomic mass of nickel at 58.69, the next element in the periodic table . This peculiarity also exists between argon and potassium and between tellurium and iodine .

### Chemical properties

Its chemical behavior is similar to that of iron and nickel , and it is resistant in air through passivation ; it is only by oxidizing acting acids dissolved. With a normal potential of −0.277 V, cobalt is one of the base elements . In compounds it occurs mainly in the oxidation states + II and + III. However, the oxidation states −I, 0, + I, + II, + III, + IV and + V are also represented in compounds. Cobalt forms a multitude of mostly colored complexes . In contrast to covalent compounds , the oxidation state + III is more common and more stable than + II.

## Isotopes

Decay scheme of 60 Co

A total of 30  isotopes and 18 further core isomers between 47 Co and 77 Co are known. Natural cobalt consists entirely of the isotope 59 Co. The element is therefore one of the 22  pure elements . This isotope can be examined by means of NMR spectroscopy .

The nuclide 57 Co decays to 57 Fe via electron capture . The gamma radiation emitted during the transition to the basic state of the daughter nucleus has an energy of 122.06 keV (85.6%) and 14.4 keV (9.16%). The main application of 57 Co is Mössbauer spectroscopy to differentiate between divalent and trivalent iron.

The most durable of the unstable isotopes is 60 Co ( cobalt-60 , spin 5 + ) connected to a half-life of 5.27 years under beta decay initially in an excited state of 60 Ni (Spin 4 + ) and subsequently with emission of gamma radiation (two Gamma quanta of energy 1.17 and 1.33  MeV ) in the ground state (spin 0 + ) of this nuclide decays. For this reason, 60 Co as a source of gamma radiation for sterilization or preservation of food, the material examination ( radiographic testing ) and in cancer therapy ( " cobalt therapy used"). Other isotopes such as 57 Co or 58 Co can also be used as tracers in medicine. 60 Co is exclusively obtained artificially from 59 Co through neutron activation . Spontaneous fission sources such as 252 Cf serve as the neutron source for the production of smaller quantities , while 59 Co-pellets are exposed to the neutron flux in nuclear reactors to produce larger quantities .

The formation of 60 Co from 59 Co under neutron radiation could potentially also be used to intensify the effect of nuclear weapons, in which neutron radiation is generated by being coated with cobalt ( cobalt bomb ). In the event of a detonation, the strong gamma emitter would then be formed, which would contaminate the environment more strongly than the core explosion alone. If 60 Co is not properly disposed of but melted down with other cobalt and processed into steel , steel parts made from it can be radioactive to a harmful extent.

The Wu experiment was carried out with 60 Co , through which the parity violation of the weak interaction was discovered.

## Occurrence

Cobalt is a rare element with an abundance in the earth's crust of 0.004 percent. This puts it in thirtieth position in the list of items sorted by frequency. Elementary it occurs only extremely rarely in meteorites and in the earth's core . Cobalt is found in many minerals , but mostly only occurs in small amounts. The element is always associated with nickel, often also with copper, silver, iron or uranium . Nickel is about three to four times as common as cobalt. Both metals belong to the siderophilic elements and are characteristic of basic and ultra-basic magmatites .

Cobalt is found as a trace element in most soils. There are a number of cobalt ores in which the cobalt has accumulated through weathering or other processes. The most important are: cobaltite (obsolete cobalt gloss ; CoAsS) linnaeite and Siegenit (obsolete and misleading cobalt nickel gravel ; (Co, Ni) 3 S 4 ), Erythrin (obsolete cobalt bloom ), Asbolan (obsolete Erdkobalt ) Skutterudit ( smaltite , Smaltin , CoAs 3 ) and heterogenite (CoOOH). The cobalt content of the sulfidic ores is low, mostly only 0.1–0.3 percent.

The world's known cobalt reserves are 25 million tons . The most important ore deposits are in the Democratic Republic of the Congo and in Zambia , where cobalt occurs together with copper , as well as in Canada , Morocco , Cuba , Russia , Australia and the USA . Another 120 million tons of cobalt are believed to be in the earth's crust on the floors of the Atlantic , Pacific and Indian Oceans . The cobalt occurs there in manganese nodules together with manganese , copper and nickel and can be obtained as a metal alloy in a smelting reduction furnace.

Due to the importance of cobalt in the manufacture of electronic devices, there could be a shortage of supply in the coming years.

## Extraction and presentation

Cobalt ore
Electrolyte cobalt, purity 99.9%

Cobalt is mainly extracted from copper and nickel ores . The exact method of extraction depends on the composition of the original ore. First of all, some of the iron sulfides ( FeS and FeS 2 ) present are converted into iron oxide by roasting and then slagged with silicon dioxide as iron silicate . The so-called raw stone is created , which in addition to cobalt also contains nickel, copper and other iron as sulfide or arsenide . Further sulfur is removed by roasting with sodium carbonate and sodium nitrate . Sulphates and arsenates are formed from part of the sulfur and arsenic , which are leached with water. The corresponding metal oxides remain and are treated with sulfuric or hydrochloric acid . Only copper does not dissolve, while nickel, cobalt and iron dissolve. With chlorinated lime , cobalt can then be selectively precipitated as cobalt hydroxide and thus separated. This is converted into cobalt (II, III) oxide (Co 3 O 4 ) by heating and then reduced to cobalt with coke or aluminum powder :

${\ displaystyle \ mathrm {Co_ {3} O_ {4} + C \ longrightarrow 3 \ CoO + CO}}$
${\ displaystyle \ mathrm {CoO + C \ longrightarrow Co + CO}}$

The majority of cobalt is obtained by reducing the cobalt by-products of nickel and copper mining and the smelting . Because cobalt is typically a by-product, the supply of cobalt is highly dependent on the economics of copper and nickel mining in a particular market.

There are several methods of separating cobalt from copper and nickel, depending on the concentration of cobalt and the exact composition of the ore used . One method is foam flotation, in which surfactants bind to various ore constituents, which leads to an enrichment of cobalt ores. Subsequent roasting converts the ores into cobalt (II) sulfate and oxidizes copper and iron . By washing out with water, the sulfate is extracted together with the arsenates . The residues are further leached with sulfuric acid , resulting in a copper sulfate solution . Cobalt can also be leached from the copper melt.

### States with the largest production volume

Development over time of cobalt extraction (blue) and production (red)
Cobalt production by states in tons
country 2006 2013 2016
DR Congo 22000 54000 66000
China 1400 7200 7700
Russia 5100 6300 6200
Brazil 1000 3000 5800
Australia 6000 6400 5100
Zambia 8600 5200 4600
Cuba 4000 4200 4200
Philippines 3000 3500
New Caledonia 1100 3190 3300
South Africa 3000 3000
Morocco 1500 1700
remaining countries 1200 8000 8300
total 57,500 110,000 123,000

### Cobalt producers

In many cases, cobalt is not refined in the countries in which cobalt ores are mined. The following table from the Cobalt Development Institute (CDI) lists the producers of metallic cobalt and cobalt salts and their production quantities in tons:

Surname country 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
CDI
co-
members
Ambatovy Madagascar 0 0 0 0 0 0 0 0 0 0 2083 2915 3464 3273
BHPB / QNPL Australia 1800 1900 1400 1600 1800 1600 1700 2141 2631 2369
CTT Morocco 1431 1593 1613 1405 1591 1711 1600 1545 1788 1314 1353 1391 1722 1568
Eramet France 181 199 280 256 305 311 368 302 354 326 308 219 133 119
Freeport Cobalt, formerly OMG Finland 7990 7893 8170 8580 9100 8950 8850 9299 10441 10547 10010 11452 8582 11187
Gécamines DR Congo 1200 735 600 550 606 300 415 745 650 870 700 500 400 400
Glencore , Katanga DR Congo 2800 2900 0
Glencore, Minara Australia 2900 3300 3200
Glencore, Mopani Copper Zambia 0 0 0
Glencore, formerly Xstrata Norway 4556 4670 5021 4927 3939 3719 3510 3208 3067 2969 3400 3600 3100 3500
ICCI Canada 3141 3225 3391 3312 3573 3428 3721 3706 3853 3792 3319 3210 3733 3693
Rubamine India 0 517 579 200 45
Sumitomo Japan 379 429 471 920 1084 1071 1332 1935 2007 2542 2747 3654 4259 4305
Umicore Belgium 1704 2947 3298 2840 2825 3020 2150 2600 3187 4200 5415 5850 6306 6329
Vale Inco Canada 1000 1562 1563 1711 2033 2200 1193 940 2070 1890 2240 2051 1858 1851
Chambishi Metals Zambia 4570 3769 3648 3227 2635 2591 235 3934 4856 5435 5000 4317 2997 4725
Total CDI 27,952 28,922 29,455 29,328 29,491 28,901 25,074 30,872 35,483 36,454 36,620 44,859 42,754 44,150
Non-
CDI
co-
members
China 4576 8000 12700 12700 13245 18239 2544 35929 34969 29784 36062 39292 48719 45046
India 255 545 1220 1184 980 858 1001 670 720 600 250 100 150 100
Glencore, Katanga DR Congo 0 0 0 0 0 749 2535 3437 2433 2129 2300
Kasese Uganda 0 457 638 674 698 663 673 624 661 556 376 0 0 0
Glencore, Minara Australia 2039 1979 1750 2096 1884 2018 2350 1976 2091 2400 2700
Glencore, Mopani Copper Zambia 2050 2022 1774 1438 1700 1450 1300 1092 1100 230 0
Norilsk Nickel Russia 4654 4524 4748 4759 3587 2502 2352 2460 2337 2186 2368 2302 2040 3092
QNPL Australia 2281 2519 1850 0
South Africa 285 300 214 257 307 244 236 833 840 1100 1294 1332 1300 1101
Votorantim Brazil 1097 1155 1136 902 1148 994 1012 1369 1613 1750 1653 1350 1300 400
DLA United States 1987 1632 1199 294 617 203 180 −8 0 0 0 0 0 0
Total non-CDI 16,943 20,614 25,379 24,304 24,166 27,920 37.183 48,382 46764 40,735 49.284 46,895 55,359 49,739
total 44,895 49,536 54,834 53,632 53,657 56,821 59,851 79,252 82,247 77.189 85.904 91,754 98.113 93,889

Notes A:

1. a b not a CDI member since 2013
2. a b c estimated
3. a b c d CDI member since 2014
4. CDI member from 2009 to 2013
5. including Umicore China
6. without Umicore China
7. including Nicomet and Rubamin (not 2009 to 2013)
8. not a CDI member since 2009
9. Defense Logistic Agency : Sale of cobalt from US strategic reserves
10. does not include quantities from manufacturers who do not publish their production

## use

Cobalt blue glass items from Bristol

Cobalt was first used in the form of oxides , sulfates , hydroxides or carbonates for heat-resistant paints and pigments , e.g. B. used for painting porcelain and ceramics (see also smalts and blue color works ). This was followed by the most famous decorative application in the form of blue cobalt glass . After 1800 the cobalt aluminate (CoAl 2 O 4 ) was produced industrially as a strong color pigment.

Today cobalt is used as an alloy component to increase the heat resistance of alloyed and high-alloy steels , especially high-speed steel and superalloys , as a binder phase in hard metals and diamond tools (see: Widia ). Its use as an alloying element and in cobalt compounds makes it a strategically important metal. (See Vitallium : implants , turbine blades , chemical apparatus.) Cobalt steels are used e.g. B. for highly stressed work parts that have to withstand high temperatures, such. B. valve seat rings in internal combustion engines or guide vanes in gas turbines .

Cobalt- based superalloys have historically consumed most of the cobalt produced. The temperature stability of these alloys makes them suitable for turbine blades for gas turbines and aircraft engines , although single crystal nickel-based alloys outperform. Cobalt-based alloys are also resistant to corrosion and wear , so like titanium they can be used to make orthopedic implants that will not wear out over time. The development of wear-resistant cobalt alloys began in the first decade of the 20th century with the stellite alloys , which contained chromium with different proportions of tungsten and carbon . Alloys with chromium and tungsten carbides are very hard and wear-resistant. Special cobalt-chrome- molybdenum alloys such as Vitallium are used for prosthetic parts. Cobalt alloys are also used in dentures as a useful substitute for nickel , which may be allergenic . Some high speed steels also contain cobalt to increase heat resistance and wear resistance. The special alloys of aluminum , nickel, cobalt and iron , known as alnico , as well as samarium and cobalt (samarium-cobalt magnet ) are used in permanent magnets .

Cobalt is a component of magnetic alloys, as a dryer ( siccative ) for paints and lacquers , as a catalyst for desulphurization and hydrogenation , as hydroxide or lithium cobalt dioxide (LiCoO 2 ) in batteries , in corrosion and wear-resistant alloys and as a trace element for Medicine and agriculture . Cobalt is also used in the production of magnetic data carriers such as audio tapes and video cassettes , where it is doped to improve the magnetic properties. Cobalt has been used as an alloy component for guitar strings for some time .

Lithium-ion accumulator in flat design
Nissan Leaf , best-selling electric car worldwide

Since lithium-ion accumulators came onto the market in the 1990s, cobalt has been used for accumulators , especially for mobile applications, since the lithium-cobalt oxide accumulator has a particularly high energy density. The first commercially available lithium-ion battery came onto the market as a lithium-cobalt dioxide battery from Sony in 1991. Due to the expected increasing importance of accumulators for mobile electronics and electromobility , the Federation of German Industries (BDI) advises : “Due to the high concentration of cobalt deposits in the politically unstable states of the Congo and Zambia, research into manganese and iron phosphate electrodes and Also recommended in principle in nickel electrodes that contain little or no cobalt ". In a position paper of the BDI on innovative drive technologies it is predicted: "The global raw material demand for cobalt could increase by 3.4 times by the year 2030 compared to 2006 by the increasing demand for lithium-ion batteries alone".

Lithium cobalt (III) oxide is widely used in lithium ion battery cathodes . The material consists of cobalt oxide layers with embedded lithium . During the discharge, the lithium is released as lithium ions. Nickel-cadmium batteries and nickel-metal hydride batteries also contain cobalt to improve the oxidation of nickel in the battery.

Although most of the cobalt was used in batteries in a mobile device in 2018 , rechargeable batteries for electric cars are a more recent application for cobalt. This industry has quintupled its demand for cobalt, making it imperative to find new raw materials in more stable areas of the world. Even if the cobalt content of new batteries is declining, demand is expected to increase over the next few years as the spread of electric vehicles increases. In 2017, electric mobility accounted for 8.2% of global cobalt consumption; including all other areas of application, battery production was responsible for around 46% of cobalt consumption. As of 2019, modern batteries contain only around a third of the cobalt of older batteries due to better cell designs; the car manufacturer Tesla is already working on largely cobalt-free batteries. LiFePo batteries, such as those used for solar batteries , on the other hand, do not require any cobalt at all.

Catalysts based on cobalt are in reactions with carbon monoxide used. Cobalt is also a catalyst in the Fischer-Tropsch process for the hydrogenation of carbon monoxide to liquid fuels . In the hydroformylation of alkenes is often cobalt octacarbonyl as a catalyst, although it is often more efficient catalysts iridium - and rhodium is replaced, for. B. the Cativa process .

In the hydrodesulfurization of petroleum , a catalyst is used that is derived from cobalt and molybdenum . This process helps purify the petroleum of sulfur impurities that affect the refining of liquid fuels.

## physiology

Cobalt is part of vitamin B 12 , cobalamin , which is essential for human survival . In healthy people, this vitamin can possibly be formed directly from cobalt ions by intestinal bacteria . However, cobalamin must be bound by the intrinsic factor produced in the stomach in order to be able to be absorbed in the ileum . However, since the production site of man-made cobalamin is in the large intestine , absorption is not possible according to the current state of knowledge. The vitamin must therefore be taken in through food. Nevertheless, a daily intake of 0.1 μg cobalt is specified as a trace element for the daily requirement for adults. The lack of vitamin B 12 can lead to impaired erythropoiesis and thus to anemia . In ruminants , such a deficiency is mainly due to insufficient cobalt intake. In animal production , traces of cobalt are added to the feed if the animals have to be fed on pastures that are poor in cobalt . This is intended to counteract growth and lactation disorders , anemia and loss of appetite .

Bacteria in the stomach of ruminants convert cobalt salts into vitamin B 12 , a compound that can only be produced by bacteria or archaea . A minimal presence of cobalt in soils therefore significantly improves the health of grazing animals.

On cobalamin -based proteins use Corrin to keep the cobalt. Coenzyme B 12 has a reactive C-Co bond that is involved in the reactions . In humans, B 12 has two types of alkyl ligands: methyl and adenosyl . Methylcobalamin promotes the transfer of methyl groups . The adenosyl version of B 12 catalyzes rearrangements in which a hydrogen atom is transferred directly between two adjacent atoms with simultaneous exchange of the second substituent X, which can be a carbon atom with substituents, an oxygen atom of an alcohol or an amine . Methylmalonyl-CoA mutase converts methylmalonyl-CoA into succinyl-CoA , an important step in the production of energy from proteins and fats .

Although much rarer than other metalloproteins (e.g. zinc and iron ), other cobaltoproteins are known besides B 12 . These proteins include methionine aminopeptidase 2, an enzyme found in humans and other mammals that does not use the corrin ring of B 12 but instead binds cobalt directly. Another uncorrinated cobalt enzyme is nitrile hydratase, an enzyme in bacteria that metabolizes nitriles .

While small overdoses of cobalt compounds are only slightly toxic to humans, larger doses of 25 to 30 mg per day lead to skin, lung and stomach diseases, liver, heart, kidney damage and cancerous ulcers.

A number of cases of cobalt-induced cardiomyopathy (cobalt cardiomyopathy) occurred in Canada and the United States in the mid-1960s . 49 patients were registered in Quebec and 64 in Omaha. Symptoms included stomach pain, weight loss, nausea, shortness of breath, and coughing, among others. The mortality rate was 40 percent. Autopsies revealed severe damage to the heart muscle and liver . All patients were heavy beer drinkers, consuming 1.5 to 3 liters per day. They preferred to consume varieties from local breweries that had started adding cobalt (II) sulfate to beer as a foam stabilizer about a month earlier . The limit values ​​for cobalt in food were not exceeded. The incidence of the disease came to a standstill immediately after the breweries discontinued the cobalt (II) sulfate admixtures.

Cobalt (II) salts activate the hypoxia -inducible transcription factors ( HIF ) and increase the expression of HIF -dependent genes . This includes the gene for erythropoietin (EPO). Cobalt (II) salts could be abused by athletes to promote the formation of red blood cells .

## proof

A relatively informative preliminary sample for cobalt is the phosphorus salt pearl , which is colored intensely blue by cobalt ions. In the cation separation process it can be detected in addition to nickel with thiocyanate and amyl alcohol ; when dissolved in amyl alcohol it forms blue Co (SCN) 2 . The red-violet cobalt (II) thiocyanate in water also turns blue when mixed with acetone .

Cobalt can be quantitatively determined with EDTA in a complexometric titration against murexide as an indicator .

Cobalt is usually bivalent or trivalent in its compounds . These compounds often have strong colors. Important cobalt compounds are:

### Oxides

Cobalt (II) oxide is an olive-green salt that is insoluble in water . It forms a sodium chloride structure of space group Fm 3 m (space group no. 225) . Cobalt (II) oxide is used as a raw material for the production of pigments , in particular for the production of the pigment smalt , which is also used in the ceramic industry . It can also be used to make cobalt glass as well as Thénards blue . Cobalt (II, III) oxide is a black solid and belongs to the group of spinels .

Cobalt (II, III) oxide is an important intermediate product in the production of metallic cobalt. By roasting and leaching , cobalt (II, III) oxide is first obtained from various cobalt ores (mostly sulfides or arsenides ). This can now be reduced to the element with carbon or aluminothermically .

Cobalt (III) oxide is a gray-black solid that is practically insoluble in water. At a temperature above 895 ° C, it splits off oxygen , forming cobalt oxides such as Co 3 O 4 and CoO.

### Halides

Cobalt (II) chloride is a blue salt when anhydrous and pink when it is hexahydrate . It has a trigonal crystal structure of the cadmium (II) hydroxide type with the space group P 3 m 1 (space group no. 164) . Anhydrous cobalt (II) chloride is very hygroscopic and easily absorbs water. It changes its color very characteristically from blue to pink. The opposite color change from pink to blue is also possible by heating the hexahydrate to temperatures above 35 ° C. Because of the typical color change , it was used as a moisture indicator in desiccants such as silica gel . With the help of cobalt (II) chloride, water can also be detected in other solutions . It is also used as a so-called secret ink , as it is hardly visible as a hexahydrate in aqueous solution on the paper , but when it is heated, deep blue writing emerges.

Cobalt (II) bromide is a green, hygroscopic solid that changes to the red hexahydrate in air . It is easily soluble in water with a red color. Cobalt (II) iodide is a black, graphite-like hygroscopic mass that slowly turns black-green in air. It is soluble in water, whereby the diluted solutions look red, concentrated solutions turn red at low temperatures and all shades from brown to olive green at higher temperatures. Cobalt (II) bromide and cobalt (II) iodide have a hexagonal cadmium iodide - crystal structure of the space group P 6 3 mc (. Space group No. 186) .

### More connections

Cobalt (II) nitrate is a salt of nitric acid , formed from the cobalt cation and the nitrate anion . The brown-red and hygroscopic salt is usually in the form of a hexahydrate and forms monoclinic crystals that are readily soluble in water, ethanol and other organic solvents .

Cobalt (II) oxalate is a flammable, hardly inflammable, crystalline, pink solid that is practically insoluble in water. It decomposes when heated above 300 ° C. It occurs in two allotropic crystal structures. One has a monoclinic crystal structure with the space group C 2 / c (space group no. 15) , the other an orthorhombic crystal structure with the space group Cccm (space group no. 66) . Cobalt (II) oxalate is mainly used to make cobalt powder. The yellowish-pink tetrahydrate is used in the manufacture of catalysts .

Cobalt (II) sulfate is a violet-tinged red, hygroscopic salt in the anhydrous state . Cobalt (II) sulphate is used for the production of pigments , glazes , in porcelain painting , for toning paper ( photography ), in baths for cobalt electroplating and for trace element supplementation in aquaristics, among others.

Cobalt yellow is a fine, light crystalline powder and is used as a pigment for oil and watercolor painting .

Thénards Blue is a blue pigment made by sintering cobalt (II) oxide with aluminum oxide at 1200 ° C. It is extremely stable and has been used in the past as a dye for ceramics (especially Chinese porcelain), jewelry, and paints . Transparent glasses are tinted with the cobalt pigment smalt based on silicon dioxide .

The pigment Rinmans Green is a turquoise green powder and is mainly used for oil paints and cement paints . Rinman's green is a popular proof of zinc . Zinc oxide or zinc hydroxide is mixed with a small amount of a highly diluted cobalt nitrate solution on a magnesia channel . Rinman's green is created when glowing weakly in the oxidizing flame .

### Cobalt complexes

Ammonium cobalt (III) complexes: hexaammine cobalt (III) chloride and aquapentaammine cobalt (III) chloride

When ammonia solution is added, a cobalt (II) chloride solution initially forms a precipitate of cobalt (II) hydroxide , which dissolves in an excess of ammonia solution and ammonium chloride in the presence of atmospheric oxygen as an oxidizing agent to form various ammine-cobalt (III) complexes . The orange-yellow hexaammine cobalt (III) chloride and the red aquapentaammine cobalt (III) chloride are formed in particular .

${\ displaystyle \ mathrm {2 \ CoCl_ {2} +2 \ NH_ {4} Cl + 10 \ NH_ {3} +1/2 \ O_ {2} \ longrightarrow 2 \ [Co (NH_ {3}) _ { 6}] Cl_ {3} + H_ {2} O}}$
${\ displaystyle \ mathrm {2 \ CoCl_ {2} +2 \ NH_ {4} Cl + 8 \ NH_ {3} +1/2 \ O_ {2} \ longrightarrow 2 \ [Co (H_ {2} O) ( NH_ {3}) _ {5}] Cl_ {3}}}$

In addition, various chloroammine cobalt (III) complexes can also be formed, such as chloropentaammine cobalt (III) chloride or dichlorotetraammine cobalt (III) chloride. Some of these compounds fall out of solution . In addition, there are also ammine complexes of cobalt (II) salts, such as hexaammine cobalt (II) sulphate, which can be produced by passing ammonia gas over anhydrous cobalt (II) sulphate .

${\ displaystyle \ mathrm {CoSO_ {4} +6 \ NH_ {3} \ longrightarrow [Co (NH_ {3}) _ {6}] SO_ {4}}}$

In addition to the ammine complexes, there are numerous compounds with different ligands . Examples are potassium hexacyanocobaltate (II) (K 4 [Co (CN) 6 ]), potassium tetrathiocyanatocobaltate (II) (K 2 [Co (SCN) 4 ]), potassium hexanitritocobaltate (III) (Fischer's salt, cobalt yellow ), and complexes with organic ligands such as ethylenediamine or the oxalate ion .

One property of [Co (NH 3 ) 5 (NO 2 )] Cl (NO 3 ) is remarkable . When exposed to UV light, the micrometer to millimeter-sized crystals jump in this cobalt coordination compound and cover distances that are a thousand times their size. This is due to isomerization of the nitrite ligand (NO 2 ), which leads to tension in the crystal. This conversion of light into mechanical energy has been studied by scientists from the United Arab Emirates and Russia.

## literature

Commons : Cobalt  - collection of images, videos and audio files
Wiktionary: Cobalt  - explanations of meanings, word origins, synonyms, translations
Wiktionary: Cobalt  - explanations of meanings, word origins, synonyms, translations
Wikibooks: Internship Inorganic Chemistry / Cobalt  - Learning and teaching materials

## Individual evidence

1. a b c Harry H. Binder: Lexicon of chemical elements , S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
2. The values ​​for the properties (info box) are taken from www.webelements.com (Cobalt) , unless otherwise stated .
3. CIAAW, Standard Atomic Weights Revised 2013
4. entry on cobalt in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 11, 2020.
5. entry on cobalt at WebElements, https://www.webelements.com , accessed on June 11, 2020.
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10. a b Entry on cobalt in the GESTIS substance database of the IFA , accessed on August 9, 2016 (JavaScript required)
11. Entry on cobalt in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on August 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
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